Method for feeding chemical into a liquid flow

ABSTRACT

A method to feed a chemical into a liquid flow using a feed device including a nozzle casing having an isolated mixing space including: feeding the chemical to the isolated mixing space in the feed device; feeding a mixing liquid to the isolated mixing space; mixing the chemical and the mixing liquid in the isolated mixing space to form a mixture of chemical and mixing liquid, and feeding the mixture of chemical and mixing liquid to the liquid flow.

This application is a divisional application of U.S. patent applicationSer. No. 10/574,695 filed Mar. 5, 2007 which is a U.S. national phase ofinternational application PCT/FI2004/000586 filed 5 Oct. 2004 whichdesignated the U.S. and claims benefit of Finnish Application No.20031468 filed 8 Oct. 2003, the entire contents of each are herebyincorporated by reference.

BACKGROUND

The present invention is related to a method and apparatus for feedingchemical into a liquid flow. The method and apparatus of the inventionare particularly well applicable to feeding of very small chemicalvolumes in precise amounts into large process liquid flows.

Naturally, there is practically an innumerable amount of prior artmethods of feeding various chemicals into liquid flows. However, thesemethods may be divided into a few main categories as can be seen fromthe following. Firstly, it is quite possible to just let the liquid tobe added flow freely into a second liquid without employing any specialregulation or mixing means. This method of adding cannot be employed insituations where the mixing ratio or the uniformity of the mixing isimportant. Neither can it be employed in situations where the price ofthe chemical to be added is of significance.

The next applicable method is to feed the chemical in a precise ratio tothe liquid flow, whereby correct and economical dosage is obtained.However, even in this case one has to take into account that usually thedosage of the chemical is slightly excessive compared to the optimaldosage, because the mixing is known to be inadequate. The mixing may beimproved, though, by feeding the chemical, e. g., through a perforatedwall of a flow channel, whereby at least the chemical to be mixed may bespread throughout the entire liquid flow. As the last example, asituation may be discussed, where the chemical is fed in a preciseproportion either into the liquid flow upstream of the mixer or throughthe mixer itself. In that case, the efficiency of the mixing of thechemical into the liquid flow is totally dependent on the mixer design.

Finnish patent no. 108802 discusses as an essential case of mixingrelated to paper manufacture the mixing of a retention aid into fibersuspension flowing to the head box of a paper machine. In papermanufacture, retention chemicals are used especially in order to improvethe retention of fines at the wire section of a paper machine. In theFinnish patent mentioned the mixing device is in fact a conical nozzlewith an inlet for the retention chemical. The mixing device isfunctioning and efficient both in the mixing of retention chemicals andother chemicals in the short circulation of a paper machine and also inother applications in the paper and pulp industry. However, it has beennoticed in connection with some applications that various solidsubstances carried with the feed and/or dilution liquid tend toaccumulate in the device. In other words solid material tends accumulatein the device parts converging in the flow direction, which graduallyharms the flow profile, the flow itself and in the end tends to clog thedevice. FI patent application no. 20021350 describes a self-cleaningchemical feed nozzle. In other words when the nozzle starts to becomeclogged a change take place in its flow conditions which causes areaction of the nozzle to open wider the cross-sectional flow area ofthe flow channel in which the solid material in question flows with thefiber suspension; as a result of this the solid particles attached tothe channel can get loose from the nozzle and flow on.

In this kind of applications, i. e. feeding for example retentionchemicals into a fiber suspension, the mixing devices and the nozzlesdescribed in the publications mentioned work well but in cases whereonly very small amounts of chemicals are needed in relation to thesuspension flow to be fed, the operation of the these nozzles is not thebest possible for example because they cannot guarantee an adequatelyhomogenous mixing of the chemical into the process liquid flow becauseof the small volume of the chemical.

SUMMARY

In order to solve, among other things, the problem described above, anew type of a chemical feeding device has been developed the structureof which is very favorable in feeding small chemical amounts into aliquid flow. The feeding device according to the invention includes athin pipe-like duct disposed preferably inside the feeding device/nozzleso that the desired amount, in this case as small an amount as possible,of chemical can be mixed evenly into the process liquid flow. Thepipe-like duct feeding the chemical supplies the chemical into a specialnozzle of the feeding device which is preferably designed to have a kindof an isolated mixing space where the chemical and mixing liquidsupplied to the feeding device through an inlet of its own are mixed andfrom which they only after this mixing are fed through openings in themixing space at first into the feeding liquid and after that aided bythe feeding liquid mentioned to the flowing process liquid. The mixingand the dilution of the chemical to a chemical solution before it is fedto the process liquid flow pipe ensure uniform mixing of the chemicalinto the process liquid. As a result of this, the volume of the chemicalto be fed into the feeding device can be of the order of even less thanhalf a percent of the rest of the liquids supplied into the feedingdevice, which are the mixing liquid and the feeding liquid supplying themixing liquid and the chemical into the liquid flow. If desired, severalfeeding devices according to the invention instead of one, may bedisposed in connection with the process liquid flow duct.

The structure of the feeding device according to the invention, moreprecisely expressed the isolated mixing space provided at the end of themixing liquid feed pipe, improves the mixing of the chemical also inanother way. When hitting the wall of the isolated mixing space theliquid chemical is “dispersed” evenly to the whole interior of theisolated mixing space of the nozzle and is mixed and diluted morehomogenously into the mixing liquid. In addition to this structure thefeeding device can further include a kind of an additional counter piecewhich, when disposed in the middle of the mouth of the pipe-like ductfeeding the chemical, further improves the mixing to the other liquidsto be fed and further to the liquid flow to be fed

The chemical can be fed into the feeding device according to theinvention without separate dilution. In other words the dilution takesplace with the mixing liquid in the isolated mixing space of the feedingdevice. This solution dispenses among other things with the need to useseparate dilution vessels, reduces the consumption of fresh water andthus reduces the operation and maintenance costs. On the other hand, itis possible also to dilute the chemical before it is supplied to thefeeding device if so desired.

The feeding device according to the invention may be used for example inthe feeding of chemicals, such as for example TiO2, optical brighteners,paper dyes and silicates, into the flowing process liquid, only tomention a few chemicals. Thus the feeding device according to theinvention is applicable in all processes into which the chemicalsmentioned must be supplied, in particular when the amount of thechemical is very little compared with the total flow of suspensionflowing to the process. As advantageous examples, only, of the processesmay be mentioned for example fiber suspension flows of paper mills,thickening processes of various sludges, recycling fiber processes,bleaching processes and in general processes where feeding of chemicalin particular in very small amounts into filtrate, fiber suspension,sludge or the like is necessary.

The mixing device according to the invention allows using as the feedingliquid with which the chemical is supplied into the process liquid, forexample into fiber suspension, the same fiber suspension into which thechemical is to be fed. Of course also more dilute suspensions, variousfiltrates or corresponding or mere fresh water can be used as thefeeding liquid in the feeding device of the publication. The mixingliquid may also be any liquid from the process itself of fresh water.Thus all the liquid obtained from another process stage that can be usedin the feeding of the chemical, saves at the same time fresh water andthus for example reduces the consumption of fresh water of the mills.

Other characteristic features of the method and the feeding device ofthe invention are disclosed in the appended patent claims.

DESCRIPTION OF THE DRAWINGS

In the following, the method and the apparatus according to theinvention are disclosed in more detail with reference to the appendedfigures, where

FIG. 1 illustrates a prior art chemical feeding apparatus;

FIG. 2 illustrates an other prior art chemical feeding apparatus; and

FIG. 3 illustrates chemical feeding apparatus according to a preferredembodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates schematically a mixing device according to apreferred embodiment of FI patent no. 108802. The mixing apparatus 34according to FIG. 1 is, in fact, a nozzle comprising preferably anessentially conical casing 50, flanges 52 and 54 arranged into it andpreferably, but not necessarily, placed at its opposite ends, and aconduit 56 for the retention chemical. The mixing apparatus 34 isconnected by a flange 52 to a dilution medium pipe 44 and by a flange 54to a fiber suspension flow duct. In the arrangement according to thefigure, the casing 50 of the mixing apparatus 34 is converging from theflange 52 towards the flange 54, an opening 58 of the mixing apparatusbeing located inside the flange 54. The purpose of the conical form ofthe casing 50 is to accelerate the medium flow in the mixing apparatus34 so that the velocity of the jet discharging from the mixing apparatus34 into the fiber suspension flow is at least five times the velocity ofthe fiber suspension flow. In the embodiment according to the figure,the retention chemical feeding conduit 56 is preferably tangential inorder to ensure that retention chemical discharging through the opening58 of the mixing apparatus 34 into the fiber suspension flow isdistributed homogeneously at least on the whole periphery of the opening58. Inside the mixing apparatus 34 there is a hollow member 60 arrangedcentrally inside the mixing apparatus 34, into which member theretention chemical is guided from the conduit 56. In other words, theconduit 56 pierces the conical wall 50 of the mixing apparatus 34 andfurther leads via the annular space between the cone 50 and the member60 into the member 60, at the same time preferably carrying the member60 in its place. The member 60 is pierces in the axial direction by ahole 62, into which mixing liquid is brought via a valve 164 and a duct162; thus the mixing liquid can flow from inside the chemical flow tothe fiber suspension flow duct. The retention chemical flow guidedtangentially into member 60 turns in the form of a spiral flow towardsthe opening 58 of the mixing apparatus, where there is at the lower endof the member 60 (according to the figure) an annular opening 64 for theretention chemical, wherefrom the retention chemical is discharged as afan-shaped jet into the fiber suspension together with the feed liquiddischarging from outside the opening 64 and the mixing liquiddischarging from the inside of the opening 64 through the hole 62. Thefigure clearly shows that the retention chemical is not in any contactwith the mixing liquid before it is discharged through the opening 64into the fiber suspension flow duct.

FIG. 2 illustrates another prior art feed nozzle 34. It comprises,starting from the bottom of the figure, in other words from the liquidflow duct 70, an essentially cylindrical nozzle casing 80 the end ofwhich facing the liquid flow duct has a conically converging portion 82.The converging portion 82 ends at a central feed opening 84, whichcontinues to the direction of the flow duct 70 in apparatus 86 forattaching the feed nozzle 34 to the liquid flow duct 70. The side wallof the nozzle casing 80, preferably the cylindrical portion thereof, hasbeen provided with an opening 88 communicating with a feed liquid ductconnection 144 for supplying feed liquid into the mixing nozzle 34. Theend of the nozzle casing 80 opposite the flow duct 70 has been providedwith a round central opening 90 and with a pressure medium cylinder 92forming an extension of the nozzle casing 80 while the other end of thepressure medium cylinder 92 is the end 94 of the nozzle casing locatedopposite the flow duct. At the opposite end of the pressure mediumcylinder 92 there is an end plate 96 with a central round opening 98like in the upper end of the nozzle casing 80.

Both chemical and mixing liquid feed apparatus 100 extend to the nozzlecasing 80 from above through the openings 98 and 90 in the ends 96 and94 mentioned above. These feed apparatus include among other things achemical feed duct 102 which has a flow connection with the chemicalconduit 56 and a mixing liquid feed duct 104 which in turn communicateswith a mixing liquid feed conduit 162, which in this embodiment islocated centrally inside the chemical feed duct 102; the feed ducts 102and 104 being attached to each other at the upper end. The chemical feedduct 102 is preferably cylindrical for the most of its length as in thisembodiment it functions at the same time as a piston rod of the pressuremedium cylinder 92. A piston disc 106 sealed relative to the pressuremedium cylinder 92 and secured to the outer surface of the chemical feedduct 102 has been provided to serve as the piston itself. Naturally boththe ends 94 and 96 of the pressure medium cylinder 92 have been providedwith suitable sealing to ensure the operation of the cylinder.

The chemical feed duct 102 has at the lower end of it, in other words atthe end facing the fiber suspension flow duct 70 and extending insidethe nozzle casing 80, a conical converging portion 108 which isessentially located at the conical portion 82 of the nozzle casing 80and the coning angle is of the same order as that of the conicalconverging portion 82 of the nozzle casing 80. The mixing liquid feedduct 104 in turn runs centrally inside the chemical feed duct 102 andextends to a distance outside the conical converging portion 108 of thechemical feed duct 102. The figure further illustrates how the chemicalfeed duct 102 continues as a cylindrical nozzle duct 110 after theconverging portion 108 so that a narrow slot is created between the wallof the mixing liquid feed duct 104 and the nozzle duct 110; in the slotthe velocity of the chemical flow is increased to the required level forfeeding to the fiber suspension flow.

In the normal state the feed nozzle is in the operation positionillustrated in FIG. 2; thus both the nozzle duct 110 of the chemicalfeed duct 102 and openings 122 in the mixing liquid feed duct 104 arelocated outside the nozzle casing 80 essentially to the level of thewall of the fiber suspension flow duct. In the flushing position thepressure medium supplied to the pressure medium cylinder 92 via theopening 116 moves the chemical and mixing liquid feed apparatus 100 bymeans of the piston disc 106 upwards so that the distance between theconical portions 82 and 108 increases and the end 118 of the mixingliquid feed duct 104 rises so high that the feed liquid flow flushes allimpurities or solid particles via the opening 84 from between theconical portions to the fiber suspension flow duct.

After a certain time, preferably the flushing time is about 1-6 seconds,pressure medium is fed to the cylinder from the opening 120 in theopposite end of the pressure medium cylinder 92, and the piston disc 106presses the chemical and mixing liquid feed apparatus 100 back to theoperation position. The function described above is guided either bypressure, the pressure difference or volume flow of the feed liquid.

FIG. 3 illustrates a preferred embodiment of the feed apparatus, i. e.,feed nozzle 34, of the present invention. It comprises, starting fromthe bottom of the figure, in other words from the liquid flow duct 70,an essentially cylindrical nozzle casing 80 the end of which facing theliquid flow duct has a conically converging portion 82. The convergingportion 82 ends at a central feed opening 84, which continues to thedirection of the flow duct 70 in apparatus 74 and 76 for attaching thefeed nozzle 34 to the liquid flow duct 70. The side wall of the nozzlecasing 80, preferably the cylindrical portion thereof, has been providedwith an opening 88 communicating via a duct 144 and a valve 42 with thefeed liquid feed duct for supplying feed liquid into the feed nozzle 34.

A mixing liquid feed duct 142 forms together with a chemical feed duct162 the cylindrical upper portion of the feed apparatus 34. Both thefeed ducts 142 and 162 extend inside the nozzle casing 80 up to theliquid flow duct 70. The location of the end of the feed ducts isadjustable in relation to the liquid flow duct 70 so that the end of theducts extends preferably inside the flow duct. The end of the nozzlecasing 80 opposite the flow duct 70 is provided with an end part 94having a round central opening 90 for the feed duct 142. The upperportion formed by the feed duct 142 is provided with a flange 136 and amovable screw/nut connection 138 or a corresponding member by means ofwhich the upper portion (feed duct 142) and the lower portion (nozzlecasing 80) of the feed apparatus 34 are attached to each other. Inaddition to feature that the parts 136 and 138 secure the upper and thelower portions to each other the adjustable screw 138 may be used foradjusting the position of the mixing liquid 142 and the chemical feedduct 162 of the feeding device 34 in relation to the liquid flow duct70.

The adjustability of the feed device 34 and the structure of securingmeans 74 and 76 allow the use of the feed device 34 with process liquidducts 70 of various thicknesses, in other words the device can besecured to these ducts.

The side wall of the feed duct 142, preferably the cylindrical portionthereof, at a location outside the end parts 94 and 136, the nozzlecasing 80 and the feed liquid feed opening 88 as seen from the flow duct70, has been provided with an opening 56 for the mixing liquid to be fedto the feed device 34. The feed opening 56 communicates via a mixingliquid conduit 146, which in this embodiment is preferably tangential inrelation to the feed device 34, and an adjustable valve 44 with themixing liquid feed pipe for supplying mixing liquid into the feed device34.

The chemical feed duct 162, which is preferably a very thin pipe forfeeding small chemical volumes, extends in this embodiment of theinvention to the feed device 34 from above. The feed duct 162 is also inthis embodiment bent at a location above the feed device 34 to the samedirection as the connections 144 and 146 for feed and mixing liquids.The volume of the chemical to be fed may be adjusted for example with avalve 46 located in the chemical feed duct 162. The chemical feed duct162 has been secured to an elongate outer end 22 of the feed device 34with a securing means 20.

The feed duct 162 communicates with the mixing liquid feed duct 142 bybeing located in this embodiment centrally inside the mixing liquid feedduct 142 and extending close to the special nozzle part 150 of the feedduct 142 which nozzle part in turn is adjustable to extend inside theprocess liquid flow duct 70.

In this embodiment of the invention the chemical feed duct 142 has atthe lower end of it, in other words at the end facing the fibersuspension flow duct 70 and extending inside the nozzle casing 80, aconical converging portion 148 which is essentially located at theconical portion 82 of the nozzle casing 80 and its coning angle is ofthe same order as that of the conical converging portion 82 of thenozzle casing 80. The conical converging portion 148 of the mixingliquid feed duct 142 does not extend quite to the lower end ofconverging portion 82 for the feed liquid but the feed duct continuespreferably as a cylindrical duct 116 inside the feed opening 84 wherebythe cross-sectional flow area between these parts reduces in the flowdirection caused an increasing in the flow velocity of the feed liquid.The flow velocity of the mixture of the chemical to be fed into theprocess liquid flowing in the process liquid flow duct 70 and the feedliquid is at the feed moment at least five time the speed of the processliquid flow.

The cylindrical duct 116 at the lower end of the mixing chemical feedduct 142 ends at the nozzle part 150 which provides the mixing space 154isolated from the feed liquid and the flowing process liquid requiredfor the chemical mixing and from which the chemical solution (a mixtureof chemical and mixing liquid) is at first fed via openings 152 to thefeed liquid flow and further by means of the feed liquid in an even flowto the liquid flow duct 70. The isolated mixing space 154 in the nozzlepart 150 is formed for example of a cup-like “closed” end 156 of themixing liquid flow duct 142 and of the openings 152 provided at itssides. The closed end 156 is impervious to the flow of liquid. Theopenings 152 have been provided in the wall of the flow duct 142 abovethe mixing space 154 of the nozzle part 150. Via the openings 152 themixing liquid and the chemicals mixed into it are discharged practicallyin a radial fan-like flow to the feed liquid. The openings 152 may havea round, angular or for example slot-like configuration only to mentiona few examples. The thin pipe-like chemical feed duct 162 extends to theend 156 of the nozzle part 150, preferably past the openings 152. Thisembodiment guarantees a good chemical mixing result as the chemical jethits the end of the nozzle part 150 and is from there disperses evenlyto the entire mixing liquid volume and further via openings 152 to theliquid flow duct 70. The mixing and the dilution of the chemical thustake place before the feeding to the process liquid by means of the feedliquid. This ensures that precise chemical amounts are mixed into thewhole cross-sectional flow area of the process liquid. According toanother preferred embodiment of the invention a kind of an additional,for example conical, counter piece has been provided, if necessary, inthe end of the chemical feed duct 162 quite in the center of it whereby,when hitting it, the chemical jet is dispersed and mixed even moreefficiently. Another alternative is to design the end cup 156 of theduct 142 so that it divides the chemical flow coming from the duct 162evenly to different sides of the duct 162 for example by providing thebottom of the end cup at a central position relative to the duct 162with a conical or corresponding bulge converging towards the duct.

Preferably the nozzle part 150 of the mixing liquid flow duct 142 andthe mixing space therein are located inside the process liquid flow duct70 or at least in the close vicinity of the inner surface of the flowduct 70 mentioned so that the mixing of the chemical to the mixingliquid takes place 0.5 seconds, at the most, before the chemicalsolution is mixed with the process liquid. Compared with the situationillustrated in FIG. 3, where the openings 152 are located just insidethe wall of the process liquid flow duct 70 (illustrated schematically),the openings 152 may be located at the annular feed opening 84 for feedliquid, thus inside the duct portion 76.

The function of the feed liquid discharging from the opening 84 of thefeed device 34 is to give the chemical solution the required velocitywhich feeds the chemical solution efficiently across the wholecross-sectional flow area of the liquid flow duct 70. The feed liquidhits mainly axially the chemical solution jet discharging from theopenings 152 in an almost radial direction, increasing the velocity ofthe chemical and improving the mixing with the process liquid flowing inthe flow duct 70. The direction and penetration of the chemical jet areadjusted by adjusting the feed device 34 with the screw 138 and the feedpressure with valves 42, 44 and 46.

As may be seen from the above, a feeding device of a new type forfeeding and mixing various chemicals in small, precisely predeterminedamounts to process liquid flows has been developed. It should also benoted that although the above description generally discusses the use ofthe feed nozzle according to the invention particularly in connectionwith applications in wood processing industry the invention may beapplied anywhere where chemicals need to be fed and mixed into a mediumflow evenly and in precise amounts. Thus, the field of application andthe scope of protection of the invention are defined by the appendedpatent claims, only.

1. A method to feed a chemical into a liquid flow using a feed deviceincluding a nozzle casing having an isolated mixing space, said methodcomprising: feeding the chemical to the isolated mixing space in thefeed device, wherein the nozzle casing is disposed at least partially inthe liquid flow; feeding a mixing liquid to the isolated mixing space;mixing the chemical and the mixing liquid in the isolated mixing spaceto form a mixture of chemical and mixing liquid, and feeding the mixtureof chemical and mixing liquid to the liquid flow.
 2. A method accordingto claim 1, wherein the chemical is mixed with the mixing liquid lessthan 0.5 seconds before the mixture of chemical and mixing liquid is fedto the liquid flow.
 3. A method according to claim 1, further comprisingfeeding the chemical and the mixing liquid to the isolated mixing spacethrough separate flow paths including one flow path disposed inside ofanother flow path.
 4. A method according to claim 1, wherein the mixtureof chemical and mixing liquid is introduced into a feed liquid beforebeing fed to the liquid flow.
 5. A method according to claim 4, whereinthe feed liquid includes a liquid extracted from the liquid flow.
 6. Amethod according to claim 1, further comprising adjusting the mixing ofthe chemical with the mixing liquid by changing a position of theisolated mixing space in relation to a duct for the liquid flow and towhich the nozzle casing is connected.
 7. A method according to claim 1,wherein the chemical includes at least one of TiO₂, optical brighteners,paper dyes and silicates.
 8. A method according to claim 1 wherein themixing liquid includes fresh water.
 9. A method according to claim 1wherein the mixing liquid includes a circulation liquid extracted fromthe liquid flow.
 10. A method according to claim 9 wherein the liquidflow includes a fiber suspension.
 11. A method to feed a chemical into aliquid flow using a feed device including a nozzle casing including anisolated mixing space, a closed end proximate to the isolated mixingspace, a chemical feed duct having a outlet at the isolated mixing spaceand a mixing liquid feed duct in fluid communication with the isolatedmixing space, said method comprising: feeding the chemical through thechemical feed duct and discharging the chemical from the outlet into theisolated mixing space; feeding the mixing liquid through mixing liquidfeed duct to the isolated mixing space; mixing the chemical and themixing liquid in the isolated mixing space to form a mixture of chemicaland mixing liquid, wherein the mixing in the isolated mixing space isimpervious to the liquid flow, and feeding the mixture of chemical andmixing liquid from the isolated mixing space to the liquid flow, whereinat least a portion of the closed end extends into the liquid flow. 12.The method of claim 11 wherein the feeding of the mixture includespassing the mixture through an opening in the mixing liquid feed duct.13. The method of claim 12 wherein the opening is offset from the outletalong the axis of the mixing liquid feed duct.
 14. The method of claim11 wherein the chemical feed duct is contained within and coaxial to themixing liquid feed duct, and the feeding of the mixing liquid and thefeeding of the chemical flow in parallel to the isolated mixing space.15. The method of claim 11 wherein the nozzle casing includes a feedliquid duct having an opening to the liquid flow, and wherein thefeeding of the mixture includes discharging the mixture from theisolated mixing space into feed liquid flowing through the feed liquidduct and through the opening into the liquid flow.
 16. The method ofclaim 15 wherein a velocity of the feed liquid flowing through openingin the feed liquid duct causes the mixture in the feed liquid todisperse across an entirety of a cross-section of the liquid flow. 17.The method of claim 11 wherein the feeding of the mixture from theisolated space to the liquid flow occurs within one-half of a second ofthe mixing of the chemical with the mixing liquid.
 18. The methodaccording to claim 11 further comprising adjusting the mixing of thechemical with the mixing liquid by changing a relative position of theisolated mixing space in relation to a duct for the liquid flow and towhich the nozzle casing is connected.
 19. The method according to claim11, wherein the chemical includes at least one of TiO₂, opticalbrighteners, paper dyes and silicates.
 20. The method according to claim11 wherein the liquid flow includes a fiber suspension.